04 Plant Nutrition Biology Notes IGCSE 2014(2)

8/20/2019 04 Plant Nutrition Biology Notes IGCSE 2014(2)

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04 – Plant nutrition

#38 The equation for photosynthesis

Photosynthesis is the fundamental process by which plants manufacture

food molecules (carbohydrates) from rawmaterials CO2 and H2O) using energy from light.

1.The equation for photosynthesis

The raw materials are CO2, H2O and light energy.

The products are glucose (starch) and O2

2. The process of photosynthesis

Green plants take in CO2 through their leaves (by diffusion).

H2O is absorbed through plants’ roots (by osmosis), and transported

to the leaf through xylem vessels.

Chlorophyll traps light energy and absorbs it.

This energy is used to break up H2O molecules, than to bond hydrogenand CO2 to form glucose.

Glucose is usually changed to sucrose for transport around the plant,or to starch for storage.

O2 is released as a waste product, or used by plant for respiration.

In this process, light energy is converted to chemical energy for

the formation of glucose and its subsequent storage.

Video: What is photosynthesis?https://www.youtube.com/watch?v=WHMLq3bqGwk

https://www.youtube.com/watch?v=WHMLq3bqGwk


http://3.bp.blogspot.com/-6KLvAFWS9Es/UOBXuxR43JI/AAAAAAAABMM/dda7DxZo5hk/s1600/photosynthesis+equation+2.png




#39 Photosynthesis investigations - Principles and Starch test

Experiments can be used to find out what factors (CO2, light, cholorophyll)are needed for photosynthesis. But first of all you need to destarch theplants. To be certain that they are thoroughly destarched, test a leaf

for starch before you begin your investigation.

Principles of investigations

1. Investigations need controls

Control plant (or leave) has all substances it needs. Test plant lacks one substance (light/chlorophyll/CO2)

2. Plants must be destarched

It is very important that the leaves you are testing should not haveany starch in them at the beginning of the experiment.

So, first of all, you must destarch the plants. Leave them inthe dark for 48 hours. The plants use up all stores of starch in itsleaves.

3. Starch test with Iodine solution

After a few hours, carry out the starch test on both plants: Iodinesolution is used; a blue-black colour on the leave is positive.

Boil the leaf in water for 30 second. This kill the cells in theleaf à break down the membrane à iodine solution gets through cellmembrane to reach starch inside the chloroplasts and react withthem.

http://3.bp.blogspot.com/-ljfto2-uhbQ/UOB1hTKklBI/AAAAAAAABOY/sv7l15uYO1I/s1600/starch+test+on+leaf+2.png



Boil the leaf in water.

Boil the leaf in alcohol (ethanol) in a water bath: The greencolour of the leaf and the brown iodine solution can look blacktogether, so you need to remove chlorophyll by dissolving it outwith alcohol. Leave it until all the chlorophyll has come out of the leaf.

Boil the leaf in alcohol.

Rinse the leaf in water: Boiling the leaf in ethanol makes it brittle,the water softens it.

Spread the leaf out on a white tile à easy to see the result. Add iodine solution to the leaf à blue- black colour is positive, starch

is present.

A leaf before (on the left) and after (on the right) starch test.

Additional resource: sjiiscience.blogspot.com

http://sjiiscience.blogspot.com/2008/07/chlorophyll-and-starch-in-leaves.html



http://2.bp.blogspot.com/-usX20evlnfo/UOByEUpVNlI/AAAAAAAABNs/Jrq1IOpUq4c/s1600/starch+test+on+leaf.png




#40 Photosynthesis investigations – chlorophyll, CO2, light tests

Investigations to see if chlorophyll, light and CO2 are needed for

photosynthesis.

1. Chlorophyll is necessary for photosynthesis

Process

Take a potted plant with variegated (green and white) leaves. Destarch the plant by keeping it in complete darkness for about 48

hours.

Expose the plant to the sunlight for a few days.

Test one of the leaves for starch with iodine solution.

Observations

- Areas with previously green patches test positive (turn blue black).

- Areas with previously pale yellow patches test negative (remain

brown).

Conclusion

- Photosynthesis takes place only in green patches because of the

presence of chlorophyll.- The pale yellow patches do not perform photosynthesis because of the

absence of chlorophyll.

http://1.bp.blogspot.com/-33q5WIDMGYs/UOFyAPjb29I/AAAAAAAABRQ/-Sceas106K4/s1600/photosynthesis+factors.jpg



2. Light is essential for photosynthesis

Process

Take a potted plant.

Destarch the plant by keeping it in complete darkness for about 48

hours.

Test one of it leaves for starch, to check that is does not contain any.

Fix a leaf of this plant in between two strips of a thick paper on leaf.

Place the plant in light for a few days.

Remove the cover from the leaf and test it for starch.

Observations

Positive starch test will be obtained only in the portion of the leaf exposed tolight and negative test in parts with paper strip.

Conclusion Light is necessary for photosynthesis.

3. Carbon dioxide is essential for photosynthesis

Process

Take two destarched potted plants.

Cover both the plants with bell jars and label them as A and B.

Inside Set-up A, keep NaHCO3 (sodium bicarbonate). It produces CO2.

Inside Set-up B, keep NaOH (Sodium hydroxide). It absorbs CO2.

Keep both the set-ups in the sunlight at least for 6 hours.

Perform the starch test on both of the plants.



Observations

Leaf from the plant in which NaHCO3 has been placed gives positive test.

Leaf from the plant in which NaOH has been kept give negatif test.

Conclusion

Plant in Set up A gets CO2 whereas plant in Set-up B does not get CO2.

It means CO2 is must for photosynthesis.

Source: mastermindtutor.com

http://demo.mastermindtutor.com/class-10/lifeprocess_teachersnote2.html






#41 Effect of Light intensity on the rate of Photosynthesis

Plants need light energy to make the chemical energy needed to createcarbohydrates. Increasing the light intensity will boost the speed of

photosynthesis. However, at high light intensities the ratebecomes constant.

Experiment

Place a pond weed Elodea upside in a test tube containing water.

Place the tube in a beaker of fresh water at 25°C. This helps tomaintain a constant temperature around the pond weed.

Place excess sodium bicarbonate (NaHCO3) in the water to give a

constant saturated solution of CO2. Place the lamp (the only light source) at distance from the plant.

Count the number of oxygen bubbles given off by the plant in 1 minute

period. This is the rate of photosynthesis at that particular lightintensity.

The gas should be checked to prove that it is indeed oxygen - relightsa glowing splint.



Repeat at different light intensities by moving the lamp to differentdistances.

Photo from passmyexams.co.uk

Graph the results placing light intensity on the x-axis.

Explanation

Light energy absorbed by chlorophyll is converted to ATP and H+

At very low light levels the plant will be respiring only notphotosynthesising.

As the light intensity increases, the rate ofphotosynthesis increases. However, the rate will not increase beyond

a certain level of light intensity.

http://www.passmyexams.co.uk/GCSE/biology/factors-affecting-rate-of-photosynthesis.html






At high light intensities the rate becomes constant, even with furtherincreases in light intensity, there are no increases in the rate.

The plant is unable to harvest the light at these high intensities andthe chlorophyll system can be damaged by very intense light levels.

Additional sources: skoool.ie passmyexams.co.uk

http://www.skoool.ie/skoool/homeworkzone.asp?id=233








#42 Effect of Temperature on the Rate of Photosynthesis

When the temperature rises the rate of photosynthesis rises also. There is

an optimum temperature at which the rate of photosynthesis is maximum.Beyond this temperature, the reaction quickly comes to a halt.

Experiment

Place a pond weed Elodea upside in a test tube containing water

at 25°C. Place the tube in a beaker of fresh water.

Place excess sodium bicarbonate (NaHCO3) in the water to give aconstant saturated solution of CO2.

Place the lamp (the only light source) at a fixed distance from the

plant.

Maintain the room temperature at 20°C.

Count the number of oxygen bubbles given off by the plant in a one -

minute period. This is the rate of photosynthesis at that particulartemperature.

http://4.bp.blogspot.com/-ze-Ia54i_NU/UOKPdTIBFTI/AAAAAAAABVE/ZCSEqG7zv0o/s1600/temperature+rate+photosynthesis.png



The gas should be checked to prove that it is indeed oxygen - relightsa glowing splint.

Repeat at different temperatures: 0°C - surround the beaker with anice jacket; greater than room temperature (25°C, 30°C, 35°C, 40°C,45°C, etc.,) by using a hot plate.

Graph the results placing temperature on the x-axis.

Explanation

At low temperature, the enzyme does not have enough energy to meet

many substrate molecules, so the reaction is slowed.

When the temperature rises, the particles in the reaction move quicker

and collide more, so the rate of photosynthesis rises also.

At the optimum temperature, the enzyme is most efficient and the rateif maximum.



At temperatures above 40°C the rate slows down. This is because theenzymes involved in the chemical reactions of photosynthesis are

temperature sensitive and destroyed (denatured) at highertemperatures.

Additional sources : skoool.ie passmyexams.co.uk

woisd.net





http://www.woisd.net/moodle/mod/resource/view.php?id=73







#43 Effect of CO2 on the Rate of Photosynthesis

When the concentration of CO2 is low the rate of photosynthesis is also low.(the plant has to spend time waiting for more CO2 to arrive). Increasing the

concentration of CO2 increases the rate of photosynthesis.

Experiment

Place a pond weed Elodea upside in a test tube containing waterat 25°C.

Place the tube in a beaker of fresh water.

Place excess sodium bicarbonate (NaHCO3) in the water to give a

constant saturated solution of CO2.

Place the lamp (the only light source) at a fixed distance from the

plant.

Maintain the room temperature at 20°C.

Count the number of oxygen bubbles given off by the plant in a one -minute period. This is the rate of photosynthesis at that particularconcentration of CO2.

The gas should be checked to prove that it is indeed oxygen - relights

a glowing splint.

Repeat at different lower CO2 concentrations by using different

dilutions of a saturated solution.

Graph the results placing CO2 concentration on the x-axis.



Explanation

The rate of photosynthesis increases linearly withincreasing CO2 concentration (from point A to B ).

The rate falls gradually, and at a certain CO2 concentration it staysconstant (from point B to C). Here a rise in CO2 levels has no

effect as the other factors such as light intensity become limiting.

http://2.bp.blogspot.com/-g0xiCBjn-Gk/UOKnTP2X0xI/AAAAAAAABbI/g9bkJuMzHUE/s1600/photosynthesis-CO2-graph.jpg



#44 Limiting factors in photosynthesis

Limiting factor is something present in the environment in

such short supply that it restricts life processes. Three factors can limit thespeed of photosynthesis - light intensity, carbon dioxide concentration

and temperature.

If a component is in low supply then productivity is prevented from reaching

maximum.

Sunlight

Light energy is vital to the process of photosynthesis. It is severelylimiting at times of partial light conditions, e.g. dawn or dusk.

As light intensity increases, the rate of photosynthesis will increase,until the plant is photosynthesising as fast as it can. At this point,

even if light becomes brighter, the plant cannot photosynthesise any

faster.

Over the first part of the curve (between A and B), light is a limitingfactor. The plant is limited in how fast it can photosynthesise because

it does not have enough light.

Between B and C, light is not a limiting factor. Even if more light is

shone on the plant, it still cannot photosynthesise any faster.

http://2.bp.blogspot.com/-x8kRDjGGtoc/UOLZ4Z_OCPI/AAAAAAAABdg/AXTebD2m18o/s1600/Limiting+factors+graphs+photosynthesis.jpg



Carbon dioxide

In photosynthesis CO2 is a key limiting factor. The usual atmosphericlevel of CO2 is 0.03%. In perfect conditions of water availability, lightand temperature this low CO2 level holds back the photosynthetic

potential.

The more CO2 a plant is given, the faster it can photosynthesise up to

a point, but then a maximum is reach.

Temperature

The chemical reactions of photsynthesis can only take place very slowly atlow temperature, so a plant can photosynthesise faster on a warm day than

on a cold one.

http://2.bp.blogspot.com/-xufJTan0sHw/UOLo6Szkr6I/AAAAAAAALJU/kTbulANGri4/s1600/photosynthesis-CO2-graph.jpg



#45 Optimum conditions for photosynthesis in Green house

When plants are growing outside, we can not do much about changing the

conditions that they need for photosynthesis. But if crops are grown inglasshouses, then it is possible to control conditions so that they are

photosynthesising as fast as possible.

CO2 enrichment

CO2 concentration can be controlled. CO2 is often a limiting factor for

photosynthesis, because its natural concentration in the air is so very low(0.04%). In a closed glasshouse, it is possible to provide extra CO2 for the

plants, e.g. by burning fossil fuels or releasing pure CO2 from a gas cylinder.

Optimum light

Light also can be controlled. In cloudy or dark conditions, extra artificial

lighting can be provided, so that light is not limiting the rate ofphotosynthesis. The kind of lights that are used can be chosen carefully sothat they provide just the right wavelengths that the plants need.

Optimum temperature

In some countries where it is too cold for good growth of some crop plants,the heated greenhouses can be used. This is done, for example, with

tomatoes. The temperature in the glasshouse can be kept at the optimumlevel to encourage the tomatoes to grow fast and strongly, and to produce a

large yield of fruit that ripens quickly.

The temperature can be raised by using a heating system. If fossil fuels areburned, there is also a benefit from the CO2 produced.

http://3.bp.blogspot.com/-fvr9s9LJ_AQ/UOfq_797V0I/AAAAAAAABjY/eA5vio0aGh8/s1600/green+house+and+photosynthesis+optimum+conditons.png



#46 Leaf structure

The leaf consist of a broad, flat part called the lamina, which is joined to the

rest of the plant by a leaf stalk or petiole. Running through the petioleare vascular bundles, which then form the veins in the leaf.

Although a leaf looks thin, its is made up of several layers of cells. You can

see these if you look at a transverse section (cross-section) of a leaf under amicroscope.

1. Cuticle:

made of wax – waterproofing the leaf

secreted by cells of the upper epidermis

2. Upper epidermis

thin and transparent – allows light to pass through

no chloroplasts are present

act as a barrier to disease organisms

http://3.bp.blogspot.com/-P8G16ij6zno/UOfw2bpTkAI/AAAAAAAALQs/EAWDkCD_aqg/s1600/leaf+stricture+veins.png



3. Palisade mesophyll

main region for photosynthesis

cells are columnar (quite long) and packed with chloroplasts to trap

light energy

receive CO2 by diffusion from air spaces in the spongy mesophyll

4. Spongy mesophyll

cells are more spherical and loosely packed

contain chloroplasts, but not as many as in palisade cells

air spaces between cells allow gaseous exchange – co2 to the cells,o2 from the cells during photosynthesis

5. Vascular bundle

this is a leaf vein, made up of xylem and phloem

xylem vessels bring water and minerals to the leaf phloem vessels transport sugars and amino acids away

(translocation)

Photo credit: Pass My Exams6.Lower epidermis

acts as a protective layer stomata are present to regulate the loss of water

vapour (transpiration)

site of gaseous exchange into and out of the leaf

7. Stomata

- each stomata is surrounded by a pair of guard cells- guard cells – control whether the stoma is open or closed- water vapour passes out during transpiration

- CO2 diffuses in and O2 diffuses out during photosynthesis

http://1.bp.blogspot.com/-E8MONkUkMaI/UOgDwJN4FFI/AAAAAAAABkI/YEZf6EdtAj4/s1600/structure+of+a+leaf.png



#47 Plant's mineral requirements and fertilisers

Plants need minerals for healthy growth.

Plant is in need for mineral ions to control chemical activities, grow, andproduce materials. The most important minerals are Magnesium ions

and Nitrates.

1.Importance of nitrate and magnesium ions

a. Nitrates

plants absorb nitrate ions from the soil, through their root hairs nitrate ions combine with glucose -----> amino acids

amino acids bond together -----> protein

deficiency causes poor growth, especially of leaves. The stem

becomes weak, lower leaves become yellow and die, while upperleaves turn pale green

Nitrates deficiency: Growth severely restricted,few stems; yellowing of older foliage.

http://2.bp.blogspot.com/-u2sPexgnfzA/UOr6dJ0C5nI/AAAAAAAABo4/6zaOpa1tWVM/s1600/plant+nitrates+deficiency.jpg

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b.Magnesium

plants absorb magnesium ions from the soil solution

used for the manufacture of chlorophyll

each chlorophyll contains one magnesium atom

deficiency makes leaves turn yellow from the bottom of the stem

upwards and eventually stops photosynthesis

Magnesium deficiency in potato plant.

(Growth fairly normal; foliage slightly pale; older leaflets develop central

necrosis, turn yellow or brown and wither prematurely).

Magnesium deficiency: yellowing between the veins of leaves.

2. Nitrogen fertilisers

Sometimes the soil is lacking of the mineral ions needed, this problem canbe solved by adding fertilisers to the soil. Fertilisers are chemical compounds

rich in the mineral ions needed by the plants. They help the plants growfaster, increase in size and become greener, they simply make themhealthier and increase the crop yield.



Ammonium Nitrate fertiliser

Intensive farming (repeatedly using the same land fro crops) removes

nitrates from the soil. These need to be replaced to prevent a drop in yield.Nitrates can be replaced in 3 ways:

applying animal manure

crop rotation – growing leguminous plants such as peas, beans and

clover every 2 or 3 years: these plants develop root nodules containingnitrogen-fixing bacteria, and the roots are ploughed into the soil,

boosting nitrate levels adding artificial fertilisers such as ammonium nitrate

Danger of overuse

Apply too much nitrogen fertiliser ----> water is drawn out of plant roots

(osmosis) ----> plant wilt/die.

Eutrophication:

Nitrates can be leached out of the soil and enter a nearby river polluting it,creating a layer of green algae on the surface of it causing lack of light in

the river thus preventing the aqua plants photosynthesising ----> death ofalgae ----> decomposers (bacteria) multiply and decay, respire using O2 ---

-> death of aquatic animals from lack of O2 = Eutrophication.

Overuse of nitrogen fertiliser can have nasty environmental

consequences.

Additional resource: xtremepapers.com

http://www.xtremepapers.com/revision/gcse/biology/plant_nutrition.php






#48 Summary of plant nutrition

Photosynthesis takes place in chloroplasts in the leaves of plants.

The word equation for photosynthesis is:

The balanced equation is:

Chlorophyll traps energy from light. In photosynthesis, this energy is

converted to chemical energy in carbohydrates.

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Photosynthesis takes place in the cells of the mesophyll layer,especially the palisade mesophyll. Leaves are thin and have a

large surface area, to speed up the supply of carbon dioxide to the

palisade cells and to maximise the amount of sunlight that hits the leafand can be absorbed by chlorophyll. Stomata and air spaces allowcarbon dioxide to diffuse quickly from the air to the chloroplasts.

Xylem vessels bring water, and phloem tubes take away the productsof photosynthesis.

Some of the glucose that is made is used in respiration, to provideenergy to the plant cells. Some is stored as starch. Some is used to

make cellulose for cell walls. Some is transported around the plant inthe form of sucrose, in the phloem tubes. Some is combined with

nitrate or ammonium ions to make proteins. Some is used to makeother substances such as fats. With the addition of magnesium ions,

chlorophyll can be made.

When testing a leaf for starch, it must first be boiled to break down

cell membranes and allow iodine solution to make contact with anystarch inside the cells. Hot alcohol will remove chlorophyll from the

leaf, making it easier to see any colour changes.

Plants need light and carbon dioxide for photosynthesis.

If either light or carbon dioxide are in short supply, they limit the rate

of photosynthesis and are said to be limiting factors. The rateof photosynthesis is also affected by temperature.

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04 Plant Nutrition Biology Notes IGCSE 2014(2)

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